Microplastics in Freshwater Ecosystems of India: Current Trends and Future Perspectives.

Microplastics (MPs)-i.e., plastic particles less than 5 mm in length-are becoming a growing environmental concern due to their potential ecotoxicological impacts on aquatic ecosystems. In India, MPs contamination is a significantly growing problem due to increased plastic production as well as its low rate of recycling. As a result, MPs research work in India has gained considerable attention in the last two decades. The objective of this study is to conduct a comprehensive review of the existing scientific literature on MPs in freshwater ecosystems (e.g., lakes and rivers) of India. A bibliographical search was used to conduct the literature review across a number of databases including ScienceDirect, Google Scholar, and ResearchGate. We found that in comparison to the marine ecosystem the source, transport, and fate of MPs in freshwater ecosystems of India are still underexplored, and we found only 18 relevant papers. This review work reveals that there is no standard procedure for separating MPs from water and sediment samples, and as a result, comparing the results was a challenging task. The larger MPs (>500 µm) in water and sediments were identified most commonly using the attenuated total reflection (ATR) Fourier Transform Infrared (FTIR) spectroscopy technique (ATR-FTIR), whereas smaller-sized MPs (<500 µm) were identified using FTIR fitted with a confocal microscope, also known as µ-FTIR imaging or chemical imaging. We found that white-colored fibers and fragments of polypropylene (PP), polyethylene terephthalate (PET), and polyethylene (PE) were the most common polymer types in the freshwater ecosystems of India. Although research on MPs in freshwater ecosystems of India has gained momentum over the past decade, the literature review reveals a limited understanding of the impact of MPs' weathering patterns, the role of biofouling, and the role of water hyacinths on freshwater ecosystem services in India. Furthermore, the fluxes of MPs to the Indian oceans are not constrained, and atmospheric transport in high-altitude mountains, which have already been made fragile by climate change, has not been fully investigated. This study, therefore, calls for additional assessments of MPs in freshwater ecosystems-particularly in the central parts of India.

Geochemical evolution of dissolved trace elements in space and time in the Ramganga River, India.

Understanding the spatiotemporal dynamics of river water chemistry from its source to sinks is critical for constraining the origin, transformation, and "hotspots" of contaminants in a river basin. To provide new spatiotemporal constraints on river chemistry, dissolved trace element concentrations were measured at 17 targeted locations across the Ramganga River catchment. River water samples were collected across three seasons: pre-monsoon, monsoon, and post-monsoon between 2019 and 2021. To remove the dependency of trace element concentrations on discharge, we used molar ratios, as discharge data on Indian transboundary rivers are not publicly available. The dataset reveals significant spatiotemporal variability in dissolved trace element concentrations of the Ramganga River. Samples collected upstream of Moradabad, a major industrial city in western Uttar Pradesh, are characterized by ~ 1.2-2.5 times higher average concentrations of most of the trace elements except Sc, V, Cr, Rb, and Pb, likely due to intense water-rock interactions in the headwaters. Such kind of enrichment in trace metal concentrations was also observed at sites downstream of large cities and industrial centers. However, such enrichment was not enough to bring a major change in the River Ganga chemistry, as the signals got diluted downstream of the Ramganga-Ganga confluence. The average river water composition of the Ramganga River was comparable to worldwide river water composition, albeit a few sites were characterized by very high concentrations of dissolved trace elements. Finally, we provide an outlook that calls for an assessment of stable non-traditional isotopes that are ideally suited to track the origin and transformation of elements such as Li, Mg, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Sr, Ag, Cd, Sn, Pt, and Hg in Indian rivers.

Occurrence, sources, and spatial distribution of fluoride in the Ganga alluvial aquifer, India.

Groundwater contamination throughout India is a global concern as it feeds more than a billion people. Of all the contaminants, fluoride (F) is one of the most widespread and well documented since its toxic nature pose serious threats to human health. In India, groundwater F concentrations have been extensively studied over the past decades. These studies have generally concluded that the groundwater F concentrations are typically higher than the drinking water standard for human health. Here, we present the occurrence, distribution, and sources of groundwater F in the Kanpur Nagar and Kanpur Dehat districts covering ~ 6000 km2 of the area in the central part of the Ganga Basin. The result revealed significant spatial variability in dissolved F concentration ranging between 0.2 and 5.2 mg/L (average 0.9 ± 0.7 mg/L, n = 172, 1 SD), which is beyond the drinking water guideline (0.5-1.5 mg/L) of the Indian Standards. We find that 31% of groundwater sampled have F content below the optimal requirement of 0.5-1.0 mg/L causing dental caries problems. The F levels only exceeded the safe drinking water limit of 1.5 mg/L in 8% of the groundwater sampled mostly in the urban regions. Fluoride distribution shows a closer resemblance with the spatial distribution pattern of electrical conductivity, and total dissolved solids demonstrate that F in the shallow alluvial aquifers is largely derived from geogenic sources. This is further confirmed by a strong positive correlation (r = 0.91, p < 0.05) observed between chloride-normalized concentration of F and the sum of geogenic elements (∑Li, Rb, Sr, Ba). We additionally performed health risk assessments, which revealed that children are most vulnerable to dental caries (commonly known as tooth decay) and dental fluorosis problems. As F concentrations show large spatial variability in the studied aquifer, we suggest that uniform application of a single de-fluoridation and fluoridation technology on an aquifer or sub-aquifer scale without a detailed well-designed groundwater F survey will have an adverse health impact on local residents as optimal level of F in drinking water may not be compromised.

Distribution and characterization of plastic debris pollution along the Poompuhar Beach, Tamil Nadu, Southern India.

The present study was carried out to determine the characteristics, distribution, and abundance of plastic debris in 25 sediment samples collected from the Poompuhar beach, southeast coast of India. The result reveals that the mean plastic debris abundance was 42 ± 27 particles/m2 dry weight (dw) (1 SD, n = 25) with higher concentrations in the river mouth. The dominant shapes in the study area were fragment (70.7%), followed by fiber (20.7%), and pellet-shaped (8.6%). The dominant colors of the plastic debris were: white-colored (47%) followed by blue (28%) and green (14%). The study further reveals that the dominant polymer type was polyethylene (PE, 63.4%), followed by nylon (PA, 16.9), polyvinyl chloride (PVC, 15.5%), polypropylene (PP, 3.1%), and polystyrene (PS, 1.1%). In the study area, the main source of plastic debris was from land-based fishing and tourism activities, and rainwater runoff from the Cauvery River.

Microplastics in the high-altitude Himalayas: Assessment of microplastic contamination in freshwater lake sediments, Northwest Himalaya (India).

In this study, we assess the magnitude, type, and sources of microplastic (MP) in lake bottom sediments collected from freshwater Anchar Lake, located in the Kashmir Valley, Northwest Himalaya. The MP identification was done on twenty-four lake bottom sediment samples under a stereo-microscope, and their polymer compositions were characterized using an Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. The study reveals that 606 ± 360 (average ± SD, n = 24) numbers of MP were present per kilogram of dry sediment samples, with fibers (91%), fragments/films (8%), and pellets (1%) dominating the shape groups. Polyamide (PA, 96%) was the dominant polymer composition present in the sediment samples, followed by polyethylene terephthalate (PET, 1.4%), polystyrene (PS, 1.4%), polyvinyl chloride (PVC, 0.9%), and polypropylene (PP, 0.7%). Polymer Hazard Index (PHI) and Pollution Load Index (PLI) were used to evaluate the quality of sediments. It was noted that high PHI values (>1000) were due to the presence of PVC polymer. According to PLI values, sediments in the Anchar lake are less contaminated with MP. We conclude that MP in the Anchar Lake have a complex source derived mostly from the automobile, textile, and packaging industries.